1. Field of the Related Art
This disclosure relates to a surgical tool, and, more particularly, to a system and method for cutting tissue by utilizing ultrasonically vibrating blades of the surgical tool.
2. Description of the Related Art
In the past few decades, considerable interest has been directed toward the use of ultrasonically activated blades and shears for the dissection, cutting, and welding of soft tissue.
It is known to cut tissue by means of ultrasonically vibrated knives or scalpels. When a scalpel cuts tissue its effectiveness is indicated by the cutting force. This derives from the pressure required to separate the structure and from the frictional drag as the blade is drawn between the cut sections. Vibrating the blade can reduce friction and may also reduce the bond strength of the tissue. Both objectives could be achieved by applying vibrations to the cutting blade in either a longitudinal or a torsional mode.
Haemostatic cutting of individual vessels and well vasculated tissue has been taught by U.S. Pat. Nos. 3,636,943 and 3,862,630. In the '943 and '630 patents, the use of ultrasonic energy in the form of mechanical vibrations is transmitted by a tool member to close off small severed blood vessels, such as in humans, by the formation of closures at the terminal portions thereof, and stop what is referred to as “ooze,” that requires constant mopping or cleansing techniques during an operation. Such tool member may be in the form of a knife ultrasonically vibrated to simultaneously sever and close off respective terminal portions of the severed blood vessels while performing surgical procedures. The tool member, of a proper configuration, may also join together layers of tissue, including the walls of unsevered blood vessels, and with respect to the latter is foreseen as replacing the “tying off” of arteries and veins currently necessary in surgery. Thus, these patents use a longitudinal mode system to activate a blade, which has roughened surfaces in order to increase frictional energy transfer during the cutting of vascular tissue.
Additionally, U.S. Pat. Nos. 5,322,055 and 6,283,981 disclose oscillatory systems with the addition of hinged passive elements designed to press the target tissue against an energized blade so as to increase the frictional drag of tissue on the blade, and, thus, increase the heating effect necessary to ensure coagulation during the cutting process.
The '055 patent relates to an ultrasonic surgical apparatus that includes a surgical instrument having a hand piece with a transducer for converting an electrical signal into longitudinal vibratory motion of a blade connected to the hand piece and an accessory releasably connected to the hand piece to enable clamping of tissue against the vibrating blade to afford improved coagulating and cutting of tissue. Scissors-like grips actuate a pivoted clamp jaw along one side of the ultrasonically vibrating blade to compress and bias tissue against the blade in a direction normal to the direction of longitudinal vibratory movement. The clamp jaw and blade are rotatable relative to one another to align a selected blade edge of a multi-edged blade with the clamp jaw for cutting and coagulating while clamping or circumferentially spacing a selected blade edge from the clamp jaw for cutting and coagulating without clamping.
The '981 patent relates to a method of designing a balanced ultrasonic surgical instrument including an ultrasonic transmission rod and an asymmetric ultrasonically actuated blade attached to the distal end of the ultrasonic transmission rod. The ultrasonically actuated blade includes a treatment portion. The treatment portion has a functional feature such as, for example, a curved blade which makes the treatment portion asymmetric. In such method, a balance portion including at least a first asymmetric balance feature is designed and positioned between the ultrasonically actuated blade and the ultrasonic transmission rod to balance out any undesirable torque generated by the treatment portion.
All of the above-described systems share the common principle of frictionally generated heating, related to cyclic vector reversal at the friction interface, to ensure that coagulation occurs simultaneously with tissue separation. In such systems, the frictionally generated heating principle is described in terms of longitudinal excitation of the cutting blade. However, pure longitudinal excitation is not the most efficient manner to transfer vibrational energy into soft tissue.
Moreover, in U.S. Pat. No. 6,425,906 and GB 2,371,492, it is noted that Young and Young first disclosed the use of different vibrational modes specifically chosen to take advantage of direct compression wave transmission into target tissue with its unique capacity to generate cavitation as the main form of energy dissipation. Specifically, such patents were the first to disclose a system and method for using torsional excitation to transfer vibrational energy into soft tissue.
For example, the '906 patent relates to a surgical tool for cutting and/or coagulating tissue that includes a piezo-electric driver to generate ultrasonic energy including torsional mode vibrations. The '906 patent also relates to a distal torsional mode end effector, which creates focused energy transmission into target tissue trapped by a hinged jaw element against an activated waveguide.
In the GB 2,333,709 patent, the use of multi-wavelength torsional mode waveguides is disclosed in relation to minimally invasive general surgical procedures. In the '709 patent, mechanisms of energy transfer are described that relate specifically to shear mode torsional systems and the conventional compression wave longitudinal equivalents. The '709 patent further discloses that excitation of a waveguide having a length greater than 7 or 8 times the half wavelength for shear mode transmission creates issues, which are exaggerated relative to those experienced in similar compression wave systems.
Thus, while it is known to use torsional excitation to transfer vibrational energy into soft tissue, it is still desirable to produce further surgical tools that effectively manipulate torsional mode excitation.